This invention relates to a device for oxygenating blood circulating in an extracorporeal circuit with a heat exchanger.
It is known that in the course of some surgical procedures it becomes necessary to circulate blood externally to the patient's body. During the extracorporeal circulation blood requires to be oxygenated and heated in order to maintain the normal body temperature, or cooled where momentarily operating in hypothermia. For this purpose, devices have been proposed, known as oxygenators, which comprise a heat exchanger capable of performing the above functions. These oxygenators are not devoid of shortcomings.
It will be appreciated, first of all, that a basic requirement of an oxygenating device is that blood flows through it in optimum conditions, both from the standpoint of enabling a good intermixing of oxygen, and from that of preventing stagnation points or the throwing of blood against the walls of the device, which could have fatal results causing hemolysis phenomena, i.e. collapsing of red cells, and from the very important standpoint of minimizing contact of blood with the walls of the device, which constitute a foreign object susceptible to become a source of contamination and other complications.
The optimization of the blood flow is of course achieved with a suitable selection of the cross-section dimensions of the passageways within the oxygenator in accordance with the blood flow rate; because of the fact that this flow rate varies in a directly proportional way to the patient's weight, conventional devices are manufactured in three different sizes, one of which is intended for newly born children, one for pediatric applications, and one for adult applications, in an attempt to approach as far as possible the optimum conditions in each case; however it is evident that the optimization thus achieved can only be a coarse one because each of the three types will have to accommodate widely different flow rates both on account of the different weights of the patients being treated and because any individual patient may involve momentarily different conditions especially when the surgical operation is carried out in conditions of hypothermia, with attendant greatly reduced blood flow rate.
Moreover, the availability of three sizes of oxygenators leads to problems in respect of supplying and inventory. To the coarse optimization of the sizes of conventional oxygenating devices as a function of the blood flow rate there is connected another negative aspect. This aspect consists in that the amount of blood which must be retained within the apparatus in order to allow priming of the apparatus, does not proportionally follow flow rate drops, but is constantly disproportionately high, thus subtracting blood from the amount required by the surgeon to face contingent situations.